Several well known systems for regulating the volumetric rate of fluid flowing in pipes and conduits generally include two basic elements: means for sensing the level of fluid and means for controlling the flow in response to the sensor "output". In one particular example, the sensor may be a simple float mechanically connected to a control gate or dam. When a change in the fluid level causes a displacement in the position of the float, the gate is repositioned to maintain the desired flow. In other systems, the pressures above and below a restriction in a conduit are sensed by a member responsive to pressure differences. The differential member is arranged to control the position of a valve within the conduit; if the pressure changes, the valve is repositioned so as to alter the valve opening, and hence maintain a constant rate of flow.
While the above-described systems may be effective in certain applications, they nevertheless suffer a significant deficiency in that either or both the sensor and the control means must physically move in order to effectuate the desired control. If either element becomes jammed or is otherwise rendered immobile, the ability to regulate the fluid flow is lost, and serious damage may ensue. The possibility of such an occurrence is underscored by virtue of the extremely deleterious environment in which the control system functions. When located, for example, in a sanitary sewer system, the mechanical elements in a prior art fluid flow control system are subject to rapid rust and detereoration unless a strict program of preventative maintenance is instituted.
In view of the foregoing, the broad object of the present invention is to provide an improved system for regulating the rate of fluid flow in a conduit or duct, wherein moving parts are not required either to sense changes in the fluid level or to control the flow rate in response to the sensor output. Additional objects are to provide such a system which is both easy and inexpensive to design, construct, install and maintain.